We will address the effects of chemical dose (exposure) on the absorption, metabolic activation, and DNA adduct kinetics for human dietary heterocyclic amines. Our goal is to determine the types and significance of DNA damage occurring at exposure levels expected from the diet. We will focus our investigations on the amino-imidazoazaarene (AIA) heterocyclic amines which are formed in meat at the ppb level during cooking. These chemicals are potent mutagens in bacterial mutation assays and are carcinogenic in mice, rats, and primates when bioassayed at the maximally tolerated doses. Since these are formed in meat they are widely consumed by the American public and may pose a substantial health risk. While these compounds have recently been shown to be carcinogenic at the maximum tolerated dose, the true health significance must be assessed at much lower exposure levels and extrapolated to humans. To answer these questions we will combine traditional methods of molecular dosimetry with a new ultra- sensitive technique for radioisotope detection. This new technique, accelerator mass spectrometry (AMS), will be used to define the toxicokinetics and DNA adduct dosimetry at actual environmental exposure levels in rodent models. We will compare the effects of dose on metabolic activation in rodents and in human tissue fractions. 32P-postlabeling will be used to validate the methodology and to identify and determine the relationships of the major DNA adducts to mutagenesis and chromosomal damage. We will also synthesize and determine the structural nature of the major adducts. Finally, the data will be used in risk assessment models to estimate the genetic and cancer risk posed from exposure to these compounds. We have already synthesized metabolic intermediates of the AIAs, and developed in vitro and in vivo models to study the activation of the AIAs to DNA damaging intermediates. We have developed methodology to use AMS in DNA adduct dosimetry. Our collaborators have developed methods to assess cytogenetic and metabolic parameters and to develop risk estimates. These tools will be easily combined and adapted to the heterocyclic amine carcinogens of interest here. The data obtained through this proposal will be important to understanding the relationships between exposure, DNA adduct formation, DNA adduct numbers and repair, and the genetic toxicities of DNA adducts at levels caused through actual exposures. Most importantly, this data will be used for assessing the risk posed from consumption of a group of heterocyclic amine carcinogens which are prevalent in the American diet.